As the network evolves to next generation network, an IP-based IMS network will provide calling services such as Voice over IP (VoIP). The capability of providing voice announcement and interactive voice response is a very important user experience for end users. For example, a user expects a charging system to provide voice announcement about subscriber account balance, awards and the like and when the balance is too low, to provide interactive voice response for performing recharging by inputting scratch-card number and PIN number, etc.
3GPP TS 32.260 standard defines that the online charging for IMS call is based on Diameter credit control protocol. In particular, an online charging client (also referred to as Diameter client) such as IMS gateway (IMSGW), application server (AS) or media resource function controller (MRFC) etc. request quota for resource usage from an online charging system (OCS) based on Ro interface; the OCS grants the quota, such as allowing the user to call for a period of time, to the user according to account profile such as the balance, and sends the quota to the online charging client via Ro interface; the online charging client controls the charging for calling according to the quota for resource usage received from the OCS.
However, because the interface to the OCS is Ro interface, the OCS cannot control IMS calls to provide voice announcement and interactive voice response to, for example, notify an end user of account profile or operate on the account profile, etc. Moreover, Diameter credit control protocol does not have the capability of providing announcement and interactive voice response, either. Thus, the existing system cannot provide charging-related voice announcement and interactive voice response.
Without voice announcement or interactive voice response, user's experience for IMS call charging is greatly impacted. This will be an obstacle for operators to deploy prepaid voice services over IMS network, such as IMS fixed line calling card solution.